Hmmm...Ive found that the major bottlenecks on lower end stuff is actually the IO DB writes/reads and not so much crypto related stuff. Sure it has a positive effect if you can speed it up, but a good 70%+ of optimizing I do is how to get data over the IO quicker and more efficiently.
What DB system do you use? MySQL? I use
http://docs.oracle.com/javase/8/docs/api/java/nio/MappedByteBuffer.html.
I have just recalled that Emunie does much more than just payments, in this case we cannot compare our solutions, because our cryptocurrency works with payments only and doesn't need to do sophisticated stuff like order matching.
MySQL and Derby for development, probably go with Derby or H2 for V1.0.
The data stores themselves are abstracted though, so any DB solution can sit behind them with minor work so long as they implement the basic interface.
That solution for you (if it fits your purpose) will be very fast, then your IO bottleneck will mainly shift to network I imagine?
Both of these methods are horridly inefficient. Cripes disk space is not at a premium. Duh!